1. Field of the Invention
This specification relates to an inner shield for a vacuum interrupter.
2. Background of the Invention
An inner shield for a vacuum interrupter, to which the present disclosure is applied, is used for a high-pressure/ultra high-pressure vacuum interrupter. As a rated voltage of the vacuum interrupter increases, a dielectric strength level required increases and accordingly the vacuum interrupter is elongated.
The high-pressure/ultra high-pressure vacuum interrupter may have limitation to improving a dielectric strength in the existing structure of having a single center shield. Considering such limitation, an inner shield structure capable of reducing the size of the high-pressure/ultra high-pressure vacuum interrupter by improving the dielectric strength has been introduced in recent time.
FIG. 1 is a longitudinal sectional view showing a structure of a typical vacuum interrupter.
As shown in FIG. 1, in the structure of the related art vacuum interrupter, a dielectric casing 1 is sealed with a fixed flange 2 and a movable flange 3, and a stationary electrode 4 and a movable electrode 5 contactably face each other within the dielectric casing 1 and are housed within an inner shield 6 fixed to the dielectric casing 1. Also, a stationary shaft 4a of the stationary electrode 4 is connected to the exterior with being fixed to the fixed flange 2, and a movable shaft 5a of the movable electrode 5 are connected to the exterior with being slidably coupled to the movable flange 3.
A bellows shield 7 is fixed to the movable shaft 5a of the movable electrode 5. A bellows 8 is disposed between the bellows shield 7 and the movable flange 3 to allow the movable electrode 5 and the movable shaft 5a to be movable in a sealed state within the dielectric casing 1.
The inner shield 6 is located at a position where the stationary electrode 4 and the movable electrode 5 are symmetric to each other when both of the electrodes 4 and 5 are completely open. The inner shield 6 prevents reduction of a dielectric strength, which is caused as metal vapor, which is dispersed upon arc generation at a breaking operation, is absorbed on an inner surface of the dielectric casing 1.
FIG. 2 is a longitudinal sectional view showing another exemplary structure of a vacuum interrupter according to the related art.
The high-pressure vacuum interrupter shown in FIG. 2 has a structure that a stationary-side sub shield 12 and a movable-side sub shield 13 are further installed at both sides of a main shield 11 in an axial direction to overlap the main shield 11. The like/similar portions to FIG. 1 have the like/similar reference numerals.
In this structure, the vacuum interrupter is formed such that a diameter at a side of an electrode of the sub shields 12 and 13 is smaller than that of the main shield 11. The vacuum interrupter further includes the sub shields 12 and 13 in addition to the main shield 11 to mitigate an equipotential distribution, thereby improving a dielectric strength.
However, in the structure of the vacuum interrupter having those sub shields, ends of the sub shields 12 and 13 are linearly formed, electric fields are concentrated on the ends of the sub shields 12 and 12, as shown in FIG. 3, which may cause a dielectric breakdown.